Hi again!
I have rewritten the patch that enabled HTML based transclusion:
https://gerrit.wikimedia.org/r/#/c/132710/
I tried to address the concerns raised about my previous attempt, namely, how
HTML based transclusion is handled in expandtemplates, and how page meta data
such as resource modules get passed from the transcluded content to the main
parser output (this should work now).
For expandtemplates, I decided to just keep HTML based transclusions as they are
- including special page transclusions. So, expandtemplates will simply leave
{{Special:Foo}} and {{MediaWiki:Foo.js}} in the expanded text, while in the xml
output, you can still see them as template calls.
Cheers,
Daniel